1. Field of the Invention
This invention relates to knife assemblies for disk-type chippers, and more particularly concerns an improved knife clamp which reduces the propensity for sawdust buildup behind the knife clamp.
2. Description of the Prior Art
Numerous log chippers have been disclosed in the prior art and tire in widespread industrial use. Various knife holding arrangements have been employed for disposing a sharpened blade outwardly from a cutting disc. For example, U.S. Pat. No. 3,892,265 to Vanek, U.S. Pat. No. 3,907,016 to Nicholson et al., and U.S. Pat. No. 3,777,793 to Miller disclose knife holding devices for use in log chippers. One well known chipper is described in U.S. Pat. No. 4,784,337 to Nettles et al. The chipper there described is of the well known Carthage-Norman design in which a vertically disposed disc rotates upon a horizontal drive shaft. The disc is covered by a removable housing, and a spout projects from the housing for receiving logs. The logs are fed end-on to a series of radially disposed knives carried by the disc. The knives are clamped in place at cutting stations around the front face of the disc. Chip slot passages extending through the disc are situated adjacent each cutting station. The wood chips cut from the logs move through the chip passages and are ejected from the rear face of the disc. The spout or feeder has a stationary bedknife that cooperates with the rotary knives so that the logs are cut into uniform chips suitable to be supplied, e.g., to a digester of a wood pulping process.
The blades of the knife assemblies are the parts of the chipper most subject to wear. Ideally the blades should be easy to replace and accurately adjust. In a typical use situation, the blades are changed about every 8 to 12 hours of service, sometimes more, depending on cutting conditions.
In the Carthage-Norman design, at each cutting station the knife assembly is comprised of a fixed knife holder securely fastened to the front face of the disc by means of threaded members such as studs or bolts. A knife, or knife assembly, is mounted at an angle of about thirty to forty-five degrees with respect to the associated chip slot. The cutting edge of the knife resides within the chip slot. The knife holder has a sloping abutment surface which contacts the front surface of the knife. A clamping member, seated within a recess in the front face of the disc, is urged toward the front face of the disc by means of threaded bolts whose heads are disposed on the rear face of the disc. A sloping front face on the clamping member is adapted to contact the rear surface of the knife, which contains the cutting edge. The knife is thereby sandwiched between the abutment surface of the knife holder and sloping front face of the clamping member.
A particular difficulty encountered in the use and maintenance of the Carthage-Norman chipper is the great frequency with which the knives must be removed for resharpening, and the difficulty in removing the blades.
The typical procedure for knife removal involves loosening the threaded bolts that forwardly urge the clamping member. Springs which interact between the clamping member and the disc are intended to pull the clamping member rearwardly, away from the knife. However, with continued use, the springs become ineffective in retracting the clamping member. When this happens, forceful hammering upon the ends of the blades, and prying manipulations are required to dislodge the blade. Eventually the clamping member must be completely removed for cleaning. This practice is time consuming and requires significant machine down-time. The beating and prying on knife blades has a deleterious effect upon the blades, often causing chips and bends which require greater grinding in the sharpening process, resulting in curtailed knife blade life. Furthermore, this process diminishes the life of the disc itself which is costly to replace, and creates a major loss of machine time.
There is also a safety concern in the process of hammering and prying knife blades loose. Often a hammer, pry bar or blade may slip or drop, causing serious injury to maintenance personnel. The difficulty of changing knife blades is perceived by those in the industry as a generally disagreeable task and therefore negatively affects employee moral and job satisfaction.
It has now been found that the ineffectiveness of the springs in retracting the clamping member is caused by the accumulation of dust behind the clamping member.
It is obvious that a knife which is easier to change could greatly improve machine and parts life expectancy, productivity, industrial safety, and worker satisfaction.
It is accordingly an object of the present invention to provide an improved knife clamp for a wood chipper substantially of the Carthage-Norman type.
It is another object of the present invention to provide a clamp of the aforesaid type which has a significantly lower propensity toward sawdust collection and buildup.
It is a further object of this invention to provide a clamp of the aforesaid type which is easily loosened to provide convenience in the removal and reinstallation of a knife blade.
It is yet another object of this invention to provide a clamp of the aforesaid type which secures an associated knife blade, and is easily retrofitted to existing chippers.
It is still another object of this invention to provide a clamp of the aforesaid type which is durable and amenable to low cost manufacture.
These and other beneficial objects and advantages will be apparent from the following description.